http://iscoresports.com/

We had a play in a game lastnight (that none of us had ever seen before)

Leadoff batter hits a liner to the gap in right center, it's a quick runner so they had rounded second by the time the F4 took the cutoff throw from F9. F4 attempted to throw to F5 but the ball hit the top of the runners helmet and bounced far enough away from F5 to allow the runner to score.

The runner had just started to slide and there was no chance of a successful tag, so it was scored as a triple, our question is how to score the opportunity to advance home as a result of the ball deflecting off the runner. Surely it isn't a throwing error on F4 because the throw was on line.....at the time we decided to score it as a triple and advance home on the throw, but that doesn't seem quite right either.

PS.....the ball remained in the field so it cannot be scored as advancing on a ball out of play

Nevermind......I found the relevant rule (at least in MLB, I assume it's the same)

Rule 10.12 (a) The official scorer shall charge an error against any fielder:

(7) whose throw takes an unnatural bounce, touches a base or the pitcher’s plate,
or touches a runner, a fielder or an umpire, thereby permitting any runner to
advance; or

Rule 10.12(a)(7) Comment: The official scorer shall apply this rule even when it appears to
be an injustice to a fielder whose throw was accurate.